Travel to the Future

 

The usual way

We should feel some awe at our ability to travel in time, but we tend to take travel to the future for granted because we do it so well.

It is conceivable that our passage into the future second by second, minute by minute, and year by year is only an illusion. It is a well-regarded philosophical view that you are, in reality, no more present at this moment than you are at all the others moments of your life, past and future.  Yet, it is nearly impossible even for philosophers to believe this outside the study or seminar room. We live with a now that moves into the future – relentlessly.

(That reality has no moving now is unbelievable, but that is not to say it is false. Sometimes what was entertained only in the seminar room is the truth as the history of physics has shown. One way to understand the idea that every other moment is really just as much now as this is one is that your consciousness at this moment is all that there is of you. The illusion that you have progressed through time results only from the memories set in by the preceding states of consciousness associated with your body. (For more on this possibility see, “Time, Relativity, and the Mayfly Self” http://lawrencecrocker.blogspot.com/2019/06/time-relativity-and-mayfly-self.html. )

Illusion or reality, the ordinary sort of future-ward time travel only gets any real attention when it is augmented in one fashion or another so that the traveler goes into the future slower or faster than contemporaries or goes farther into the future than the biology of human aging would otherwise permit.

Suspended animation

Suspended animation is a straightforward way of getting farther into the future than one’s contemporaries.  In fiction it is at least as old as Sleeping Beauty and Rip van Winkel and as new as Don’t Look Up.

Suspension is standard operating procedure in fictional voyages of colonization of extra-solar planets. In Don’t Look Up the suspended animation trip to the new world took 22,740 years. Jenifer Lawrence’s character, Aurora Lane, in Passengers, planned to use suspended animation specifically as a time travel device. The suspension of an outbound space trip followed by that of a return to earth was to reposition Aurora 250 years future-ward in earth history. A short story, the title of which escapes me, has a big-time criminal escaping punishment by entering a suspended animation capsule with its dial set for a couple of hundred years. Crime, however, does not pay. His device malfunctions, and he awakes geological eras later where he has outlived not only his enemies but absolutely everyone. The ill-gotten wealth secreted along with him proves little consolation, being inedible.

High speeds and special relativity

Heading outbound at near the speed of light out then turning back at the same speed, the celebrated space traveler might be 50 when she gets back to Earth to toast their birthday with her centenarian twin. She gets to the same future as her twin, but has gotten there faster in terms of the minutes that have passed for her.

From the Earth frame of reference, the ship-twin is always aging (in years) at half the rate of the Earth-twin. From both the ship-outbound frame and the ship-inbound frame the Earth-twin is aging at half the rate of the ship-twin. This symmetry led to the title “twins paradox” given that decidedly unsymmetrical reunion.

The crucial break in the symmetry comes when the ship turns. At the end of the outbound leg, at the speed I am assuming, in ship-time the ship-twin is 25 and her twin on Earth 12.5. At the beginning of the inbound leg, the ship-time, ship-twin is 25 and a few minutes but, Earth-twin is 87.5.  Earth-time, from the turn, Earth-twin ages from 50 to 100 at reunion and ship-twin from 25 to 50. Ship-time, from the turn, ship-twin goes from 25 to 50 while her sister’s age, from 87.5, reaches 100.

Although it is a tad weird that for ship-twin her sister is one minute 12.5 and the next 87.5, there is no paradox. Simultaneity is frame relative.  The simultaneity lines for frames going at high speeds in opposite directions are very different.

Literature for the general reader often suggests that it is the acceleration of the turn, together, perhaps with the accelerations of takeoff and landing that result in the “paradoxical” asymmetry. The takeoff and landing, however, are insignificant for the time question.  The turn is important, not because it constitutes an acceleration, but only because it is the transition between the outbound and inbound legs of the space journey. Acceleration is in the province of general relativity, but any suggestion that general relativity is essential to dissolving the twins paradox is flatly wrong.

The only essential thing here is that there are three frames, Earth, outbound and inbound.  Replace the twins with three big stopwatches. The Earth watch and Ship-Out’s watch are both started when Ship-Out passes, at its high speed, very near Earth. When Ship-Out’s clock reads 25 years, it does not change direction, but is passed by Ship-In going the opposite direction at the same speed relative to Earth. At that passing the clock in Ship-In is synchronized (at the 25 year mark) with Ship-Out’s clock.  When Ship-In finally passes by Earth, its clock reads “50,” and the Earth clock reads “100.” This duplicates the twin phenomenon with no accelerations at all. For a nice presentation of this, with the math, see https://www.youtube.com/watch?v=GgvajuvSpF4. 

High gravity and general relativity

Hanging out near enough to a black hole also slows one’s time relative to the time in regions of space far from massive objects. A high gravity twin will see a low gravity twin as getting older uniformly faster and the low gravity twin will see the high gravity as getting older uniformly slower. Taking a long black hole neighborhood vacation could be used for time travel into the future when one gets back home.

Slow time regions

In the 2017 movie Time Trap, the time regime of a remote cave moves at about two seconds per earth year. For every hour in the cave the outside world has gone through 1800 years. Our protagonists have trouble getting out as their rappel ropes (cave time) wear away in hours with the years of friction suffered by their segments outside the time frontier. There may be other works of fiction that have fast or slow time in regions not differing from their neighborhoods in any way significant to relativity, but none come to mind.

Leaps into the future

In all the cases so far surveyed, the “time traveler” is in existence simultaneously with non-travelers from the latter's frame of reference. It is always possible to say where Rip van Winkle or the ship twin or the cave explorers are from the point of view of the stay-at-homes. This need not be the case in fiction or perhaps in exotic space time geometries.   The time traveler may be nowhere for any earth-moment between the departure moment and the future arrival moment, which might be far apart. I am thinking here of the radical form in which the traveler is nowhere in any form, matter, energy, spirit, what-have-you, between e.g. 2022 and 3022.

Leaping into the future is in this way essentially different from other future bound trips, and its science and engineering might be somewhat challenging. So far as I can see, however, it would not raise any particularly interesting metaphysical issues save whether a person’s career can have a patch of non-existence, in space time terms, sandwiched between two periods of existence. This could be a problem for physical continuity theories of personal identity. Those holding some version of Locke’s memory theory, however, would not be troubled. Your consciousness and what you subsequently remembered would simply flash from your 21^st century living room to, say, a 31^st century café.

Time travel light?

Even these augmented forms of our (apparent) ordinary movement into the future may seem to be less than real, heavy duty, time travel. It is only like traveling to a part of the world you have never visited before.  You cannot use any of these methods to beat your rival to the punch with your college crush, to make a killing on the market, to pay young Hitler’s way to a Parisian art school, or to shoot your grandfather. For that you need a route that, whether or not it has a future heading phase, involves some travel towards the past.  That is the sort of time travel with which you might try to change history.

I close with what looks as if it might be an intermediate case: instead of your learning about the future by traveling there, you are the recipient of an information stream from the future.

Probing the future

Suppose we could send a cross-time transmitter into the future.  Ordinary electromagnetic waves, when processed in just the right way, propagate towards the past and carry back to us information from the future. Thunderstorms and an old television enabled communication across 25 years in the 2018 Spanish film Durante la tormenta (Mirage).  It’s a particular frequency on the dial of an old amateur radio set that permits conversations over the years between father and son in the 2020 film Frequency. I have vague memories of several other fictional instances of information, and only information, passing future to past or in both directions.

If you want to know what will happen in the future, you can find out by living long enough, with or without the aid of the strategies in the earlier paragraphs of this post. If you get future information while remaining in the past, however, you pass from the metaphysically light to the metaphysically heavy. Information from the future would be nearly as exciting and raise the same sorts of puzzles as would visitors from the future. If a traveler can shoot her own infant grandfather, the future side of an inter-temporal communication can persuade the person on the past side to commit the murder. 

So information from the future belongs in a post dealing with the mechanisms, real-world and fictional, of robust forms of time travel. That post is next but one.